This invention relates to handling of materials in layers, and especially in layers on pallets and other supporting surfaces. It relates to palletizing materials and subsequently depalletizing those materials, all with a minimum amount of manual lifting on the part of attending labor or machine operators. The invention relates specifically to novel spacing sheets which can be used to facilitate palletizing and depalletizing of thin-section materials, and especially loose stacks of printed materials such as newspapers, signatures, sheets of paper, magazines and the like; including stacks of in-process material. Individual elements of the material may be as thin as a single sheet of paper or as thick as the respective layer as a whole. Particularly with reference to newspapers and signatures, the loose stacks are typically compressible and of uneven height.
Apparatus for palletizing boxes, cartons, or other substantially solid pieces, such as bundles of newspapers, is known in the art. A conventional palletizer for boxes or cartons may use a horizontally, reciprocally movable stripper plate for carrying boxes to a position above a pallet onto which the boxes are to be loaded. The stripper plate is then withdrawn from beneath the boxes, thereby depositing them onto the pallet. Retaining means are used for preventing the boxes from moving with the stripper plate as it is withdrawn. Such retaining means commonly include a bar which abuts the sides of the boxes facing the direction of stripper plate withdrawal.
Palletizing an depalletizing apparatus are disclosed in the following U.S. Pat. Nos.
______________________________________ Paxton et al 2,243,919 Samler 2,656,047 Locke 2,875,907 Woodcock 2,875,908 Keyes 2,878,948 Lazott et al 2,937,482 Reed 2,940,617 Freeman 2,978,125 Magnuson 3,105,598 Gagnon 3,149,732 McWilliams 3,157,301 Jeremiah 3,166,203 Kampert 3,257,006 Bruce 3,278,048 Roth et al 3,389,810 Grasvoll 3,594,977 Larson 3,606,310 Brockmuller 3,637,093 Grasvoll 3,648,857 Carlson 3,669,282 Van Gal Jr. et al 3,682,338 Munroe 3,720,176 Alduk 3,833,132 Dawson et al 3,836,018 Golantsev 3,837,140 Ballard 3,884,368 Beal 3,946,883 Wilde et al 3,986,620 Kelley 4,030,618 Mabey et al 4,032,021 Schmitt 4,067,456 Zimmerman 4,159,058 Schmitt 4,162,016 Shorthouse 4,172,686 Schmitt 4,195,959 Pantin 4,205,934 Faltin 4,230,311 Donnelly 4,234,280 Meratti 4,255,074 Pulda 4,339,220 Cox 4,342,531 Sylvander 4,383,788 Ishida et al 4,397,246 Werkheiser 4,422,549 Werkheiser 4,439,084 Wise 4,477,067 Feldkamper 4,671,723 Liebel 4,708,247 as well as Fed. Rep. of Germany 3,107,495 Japan 54,129661 ______________________________________
In U.S. Pat. No. 4,704,060 Winski et al, herein incorporated by reference, there is disclosed palletizing apparatus for palletizing stacks of loose materials such as newspapers, signatures, sheets of paper, and the like. Winski et al disclose a plate and plate movement means, for depositing material onto a pallet or onto a partial load of material on a pallet. In that teaching, any underlying compressible materials may be compressed by the plate during the process of depositing the material. Both the material being deposited and the underlying material may be prevented from moving with the plate, by first and second projection means projecting into recessed portions of the top and bottom surfaces of the plate. The pallet load which results from loading a pallet as disclosed therein consists of a plurality of stacks extending from the underlying pallet, or a slip sheet thereon, to the upper extremity of the stack, typically the top of the pallet load. Within that environment of continuous stacks, unloading the material from the pallet is typically done by manual labor. In that process, the material is removed in a series of steps limited by the amount of material a person can manually lift at one time.
Alternatively, unloading might be done by a depalletizer wherein essentially an entire layer of the material is pushed, or swept, off the pallet at one time. The latter case of using a depalletizer is preferred in that it reduces the chance of back injury caused by excessive manual labor at the point of depalletizing, along with the associated savings in labor and medical costs.
However, conventional palletizers do not have the capability to stack loose materials such as newspaper and the like, except as disclosed in above-mentioned U.S. Pat. No. 4,704,060 to Winski et al. And to the extent newspapers are stacked on a pallet as in Winski et al, there is not any conventionally known means for removing all of the load with known pallet unloading apparatus unless the load is quite small.
One problem with handling loose materials with a pallet unloading apparatus is that each unit of the load of material on the pallet must be acted upon in some way by the apparatus, either directly or indirectly, to affect the desired movement.
A load unit is herein defined as any article, or group of articles, of the load, requiring a separate external force to cause it to move. Thus a single loose sheet of paper is a unit as is a bound bundle of papers. For assembled documents, such as newspaper or magazine, each document is generally a unit of the load.
With sheets of paper, each sheet can be a unit of the load. With the small thickness of, for example, paper, it is easy for sheets, near the bottom of a stack, to be missed by material handling apparatus which functions by action on a side of the stack, at the edges of the sheets. Yet, efficient material handling of thin sheets typically is done through interactions at the sheet edges.
Another problem with handling stacks of loose sheet materials with a pallet unloading apparatus is that only a limited stack height can be moved by pushing on a side of the stack without undue risk of toppling the stack. So some means should be provided to limit the height of an individual stack in the pallet load without the height of the individual stack determining the maximum overall amount of material which may be placed on a pallet to make up the pallet load.
It is an object of this invention to provide novel spacing sheets, and associated methods of use, which enable the stacking by a palletizer on a pallet, of thin materials such as loose papers, magazines or the like in discrete layers; such that they can subsequently be removed from the pallet, in the same discrete layers, by an appropriately configured depalletizer.